It is always important for crop producers to estimate their soybean yields to know what to expect after harvest. There might be large variation in yield within fields and from one field to the next depending on variety selection, date of planting and field uniformity.
There are four components to soybean yield that need to be considered when estimating yield, and those are plants per acre, pods per plant, seeds per pods and seeds per pound (seed size). Plant variability and August weather can greatly influence seed size, so an accurate estimate can be difficult at times. They become more accurate farther into the growing season. Use this equation to find your yield estimate:
Plants per acre
Count the number of pod-bearing plants in 1/1,000th of an acre. In 7.5-inch row spacing, count the number of plants in 69 feet, 8 inches of row. In 15-inch row spacing, count the number of plants in 34 feet, 10 inches of row. In 30-inch row spacing, count the number of plants in 17 feet, 5 inches of row.
Pods per plant
Pod number begins to accumulate in early to mid-July and is finalized by mid-August. Count the number of pods (containing one or more seeds) from 10 plants selected at random. Divide the total number of pods by 10 to get the average number of pods per plant.
Seeds per pod
Seed fill begins shortly following pod formation, however, does not become easily distinguished within the pod until August. Count the number of seeds from 10 pods selected at random. In general, the number of seeds per pod is 2.5, but this number might be less in a stressful environmental. Divide the total number of seeds by 10 to get the average number of seeds per pod.
Seeds per pound (seed size)
Seed size is largely influenced by sunlight and rainfall in August. However, the seed fill period can be cut short for long-season varieties due to early fall frost occurrence or other late season stresses. Assume that there are approximately 3,000 seeds per pound. If the soybean plants experienced stress, seed size will be reduced, so it will take more seeds to make one pound. Use a seed size estimate of 3,500 seeds per pound if smaller seeds are expected because of late season stress.